Field of the Invention
The present invention provides a new class of thermosetting ring-opening metathesis polymerization materials based on norbornene and oxanorbornene dicarboximide moieties containing at least one acetal ester group linkage. The acetal ester group is degradable when subjected to heat or acidic aqueous hydrolysis. The polymerization materials can be used in reworkable thermosetting compositions.
Description of Related Art
Thermosetting polymers are an important class of materials and have been used in a wide range of applications because of their excellent thermal and mechanical properties, particularly as coatings, adhesives, and encapsulants. However, traditional thermosetting materials generally display good durability, poor tractability, and poor biodegradability. These characteristics limit their use particularly in those applications for which degradable or reworkable polymers are advantageous in many industries, such as in electronics, recycling, and biodegradation. For example, the reworkability of an adhesive employed in semiconductor chips is desirable because it is costly to discard a multi-chip package with a single failed chip. The use of an adhesive that will decompose to allow chip repair or replacement would be very desirable for semiconductor manufacturers. Thus, there is a need for adhesives, coatings, and encapsulants that can be reworked in many applications.
Ring-opening metathesis polymerization (ROMP), initiated by well-defined ruthenium initiators, have been shown to display excellent functional group tolerance and allows the synthesis of well-defined polymers with controlled architectures, molecular weights, polydispersities, and terminal functionalities. ROMP processing techniques have also been developed for the synthesis of thermosetting materials with well-defined crosslinked networks from mixtures of monofunctional and difunctional monomers using ruthenium initiators for applications in Resin Transfer Moulding (RTM) and Reaction Injection Moulding (RIM). By this ROMP processing technique, an excellent level of control over crosslink density and hence over material properties has been developed. The crosslinked materials produced show high values of yield strength and toughness, which are either comparable or better than the engineering polymer materials, such as polycarbonates which are not easy to synthesize and process. The ROMP thermosetting materials are thermally stable >400° C. and can be used for applications where high temperature stability is required.
A number of different types of degradable linkages have previously been studied. Polymers containing acetal or ketal groups along the main chain have been reported which are shown to degrade into low molecular weight compounds by acid-catalysed hydrolysis. Recently, thermally degradable carbamate and carbonate linkages have been introduced into epoxy-based adhesive formulations to facilitate the reworking process. Most of the degradable thermosetting materials that have been reported in the literature are based on traditional epoxy resin systems and maleimide resin systems containing acetal ester groups.